Not only engineers, but also doctors became interested in the ability of a laser beam to drill and weld various materials. Imagine an operating room where there is a CO2 laser next to the operating table. The laser radiation enters the articulated light system - a system of hollow sliding tubes, inside which the light spreads, reflecting from the mirrors. The light passes through the light guide into the output tube, which the surgeon holds in his hand. He can move it in space, freely turning it in different directions and thereby sending a laser beam to the right place. There is a small pointer at the end of the outlet tube; it serves to direct the beam - after all, the beam itself is invisible. The beam is focused at a point located at a distance of 3-5 mm from the end of the pointer. This is a laser surgical scalpel.
The focus of the laser beam concentrates energy sufficient to quickly heat and vaporize biological tissue. By moving the “laser scalpel”, the surgeon cuts through the tissue. His work is distinguished by virtuosity: here he, with an almost imperceptible movement of his hand, brought the end of the pointer closer to the tissue being cut, but here he lifted it and moved it further away; the pointer moves quickly and evenly along the cutting line, and suddenly its movement slows down slightly. The depth of the incision depends on the cutting speed and the degree of blood supply to the tissue. On average it is 2-3 mm. Often tissue dissection is performed not in one, but in several steps, cutting as if in layers. Unlike a conventional scalpel, a laser scalpel not only cuts tissue, but can also stitch the edges of the cut, in other words, it can perform biological welding.
Dissection is performed using focused radiation (the surgeon must hold the exit tube at such a distance from the tissue that the point at which the beams are focused is on the surface of the tissue). With a radiation power of 20 W and a focused light spot diameter of 1 mm, an intensity (power density) of 2.5 kW/cm 2 is achieved. The radiation penetrates the tissue to a depth of about 50 microns. Consequently, the volumetric power density used to heat the tissue reaches 500 kW/cm 3 . This is a lot for biological tissues. They quickly heat up and evaporate - the effect of cutting tissue with a laser beam is obvious. If the beam is defocused (for which it is enough to slightly move the end of the output tube from the surface of the tissue) and thereby reduce the intensity, say, to 25 W/cm 2, then the tissue will not evaporate, but surface coagulation (“brewing”) will occur. This is the process that is used to sew together cut fabric. Biological welding is carried out due to the coagulation of liquid contained in the dissected walls of the operated organ and specially squeezed into the gap between the connected sections of tissue.
The laser scalpel is an amazing tool. It has many undoubted advantages. One of them is the ability to perform not only dissection, but also stitching of tissue. Let's consider other advantages.
The laser beam makes a relatively bloodless incision, since simultaneously with the dissection of the tissue it coagulates the edges of the wound, “welding” the blood vessels encountered along the path of the incision. True, the vessels should not be too large; Large vessels must first be closed with special clamps. Due to its transparency, the laser beam allows the surgeon to clearly see the operated area. The blade of a conventional scalpel always, to some extent, blocks the surgeon's working field. The laser beam cuts the tissue as if at a distance, without exerting mechanical pressure on it. Unlike surgery with a conventional scalpel, the surgeon in this case may not be able to hold the fabric with your hand or tool. A laser scalpel ensures absolute sterility - after all, only radiation interacts with the tissue here. The laser beam acts locally; tissue evaporation occurs only at the focal point. Adjacent areas of tissue are damaged significantly less than when using a conventional scalpel. As shown clinical practice, a wound from a laser scalpel heals relatively quickly.
Before the advent of lasers, the search for methods to treat retinal detachment led to the following. It is necessary to close the retinal tear, but it is located inside the eye. They proposed a method that involved getting to the sore spot back side eyes. Why did they cut the eyelids and pull them out? eyeball out. It hung only on nerve fibers. Then thermocoagulation was carried out through the outer shell, with the help of which cicatricial fusion of the edges of the tear with the adjacent tissues was achieved. Obviously, such a complex operation requires, firstly, the virtuoso skill of the surgeon, and secondly, which is also very important, the patient’s determination to take such a step.
With the advent of lasers, research began on their use to treat retinal detachment. This work was carried out at the G. Helmholtz Institute in Moscow and at the V. P. Filatov Clinic in Odessa. The treatment method chosen was unusual. To penetrate the sore spot, you no longer need to make an incision in the eyelid and pull out the eyeball. For this, a transparent lens was used. It was through him that it was proposed to carry out the operation. For the technical implementation of the operation, a device called an OK-1 ophthalmocoagulator was developed. The device consists of a base on which power supplies and electrical equipment with controls are located. A emitting head with a ruby laser is suspended from a special hose using a flexible connection. An aiming system is located on the same optical axis with the laser, which allows you to carefully examine the fundus of the eye through the pupil, find the affected area and point (aim) the laser beam at it. For this purpose, there are two handles in the hands of the surgeon. The flash is provided by pressing a button located on one of the handles. A retractable curtain protects the surgeon's eyes during a flare. For the convenience of the operator and maintenance personnel, the device is equipped with light and sound alarms. The pulse energy is adjustable from 0.02 to 0.1 J. The operation technique itself is as follows. First, the doctor, using an optical viewer, examines the patient’s fundus and, having determined the boundaries of the diseased area, calculates the required number of flashes and the required energy of each flash. Then, following the boundaries of the diseased area, they are irradiated. The whole operation is reminiscent of spot welding metal.
Circumcision (circumcision) is surgery, during which the male penis remove the foreskin. This procedure is optional, but sometimes it is performed for various reasons: medical, religious, etc. Today, circumcision is performed using a traditional scalpel or a modern laser. Which one is better and safer?
The laser method is used not only in circumcision, but also in removing various cosmetic defects(moles, papillomas, warts, etc.), erosion of the neck of the shirt. The laser beam “burns” the layers of skin, resulting in the elimination of tumors.
During the operation, the surgeon pulls back the foreskin and pulls it tightly. He then applies a laser beam to the skin and the foreskin is excised. Self-absorbing sutures and a disinfectant bandage are applied to the site of exposure.
The operation is performed under local anesthesia and lasts 20-30 minutes. The advantages of laser circumcision are:
The only disadvantage of this procedure is its relatively high cost - scalpel circumcision is much cheaper.
The scalpel is the main surgical instrument during operations. It is a small, sharp knife used to cut and excise soft tissue.
Before surgery, the patient must be given painkiller injections. Then the penis is tied with a special thread near the head, so as not to accidentally touch tissue with a scalpel that does not need to be cut off.
After bandaging, the surgeon pulls back the foreskin and excises it with a scalpel. After this, self-absorbing sutures are applied to the site of exposure. Previously, soft tissues were blotted with tampons during surgery to stop bleeding. Today, during the operation, coagulators (electrodes) are also used, which cauterize the blood vessels and stop the bleeding.
Laser and scalpel are used to remove foreskin penis - this significantly reduces the risk of developing infectious diseases genitourinary system, the hygienic condition of the penis improves (since dirt and various secretions stop accumulating under the head, which are a favorable environment for the growth of bacteria), and sexual intercourse is lengthened.
Both methods are equally popular today. The scalpel method is chosen by many patients, since it is more familiar, and many know its principle of action. However, this method, compared to laser, has a number of disadvantages:
Both laser and scalpel circumcision can be performed at any age- the operation is performed even on infants a few days after birth.
The contraindications for both procedures are the same:
After circumcision (by any method), visit the sauna, bathhouse, swimming pool for a while, take a bath (wash in the shower), physical activity. Restrictions are usually lifted 2 weeks after surgery.
Today, laser is a safer and more modern way to remove the foreskin - it does not cause bleeding, carefully excises soft tissue, has short term rehabilitation. Therefore, it is preferable to choose this method.
The scalpel method is suitable for those who are not willing to pay a large amount for the procedure. Sometimes surgery medical indications carried out free of charge in public hospitals.
Before the operation, you will need to take some tests (for sexually transmitted infections, HIV, blood and urine tests) and undergo a series of examinations to exclude contraindications. You should also definitely consult with your doctor and decide together which method of circumcision to use - laser or scalpel. Sometimes it happens that the foreskin can only be removed with a scalpel. Also, together with the doctor, the patient decides how much foreskin can be removed.
Circumcision must be carried out experienced surgeon. The inexperience of the doctor can lead to serious complications. It is best to pay money and have the operation done in specialized clinic. It is worth considering that the clinic must have a license.
Before you is the King of Suspenders, His Majesty the Scalpel. Are there any real competitors to his “throne”? Let's find out! As the years take their toll, aging skin inevitably sags under the influence of gravity. And all of us, meekly, like sheep, are ready one fine (or rather terrible?) day to “lie under the surgeon’s scalpel.” Obviously, sagging skin is the main problem that modern cosmetology is trying to cope with. Wrinkles are probably not so scary in themselves. Sometimes they even look quite cute. On the contrary, no one likes saggy skin and is the most an unpleasant sign premature aging. As you may have heard, the internal “framework” that keeps the skin from sagging is the muscular aponeurotic layer (SMAS). It is located on the border of muscles and skin - that is, quite deep. Until recently, it was rightly believed that only a surgeon could get to it - and get there in the physical sense, by stretching and cutting off excess tissue. Yes, surgical lifting gives a quick and radical effect. But the skin itself does not become younger - its quality remains the same. And facial features can change very much - sometimes beyond recognition. These, as well as many other reasons (including the high cost of the procedure, high risks etc.) forced to look for an alternative to the scalpel. What progress has been made in in this direction? We don’t even consider chemical and laser peels - they smooth out only small wrinkles, acting no deeper than the epidermis. Golden threads, like other permanent implants, have long since dropped out of the fight - there were too many problems with them... But let’s not talk about sad things, who’s next? Injections: By injecting filler, tissue volume is redistributed as we create tension elsewhere. With slight sagging and very professional approach the effect will be good. But this is rather a disguise of the problem, rather than a solution. Thread lifting is our first real contender. Let's look at it in more detail. Contrary to popular belief, it is not intended to hold tissue by the threads themselves, since modern threads dissolve soon after insertion. The supporting effect is provided by fibrous (scar) tissue, which is formed during the insertion of threads as a result of tissue injury. Of course, these scars are invisible - they are hidden deep in the skin. However, this cannot be said to be completely harmless. The technique of introducing threads is quite complex, and only a few specialists are proficient in it. In this sense, it is close to plastic surgery. Next in line is fractional laser. By burning point by point onto the surface of the skin, it is designed to even out the skin. But despite the fact that in the advertising of clinics and beauty salons you can find various “sweet” promises, none of the manufacturers of such lasers talk about a real lifting effect. And this is correct, because fractional lasers cannot reach the SMAS and their action is limited to a maximum of 1-1.5 millimeters in depth. Due to the high temperature inside each such “point,” a thermal burn occurs and a micro-scar is formed. At large quantities With such micro-scars, the skin tightens a little (the scar tissue is denser), but most often this effect is not so pronounced as to speak of a full-fledged lifting. The disadvantages are the need for anesthesia (the procedure is very painful), the risk of post-burn hyperpigmentation, as well as a limitation on the number of procedures - after all, each time there will be more and more scars... Some of the fractional lasers burn such large spots that they are visible immediately, and what is called , with the naked eye. Even a plastic surgeon will not be able to tighten such skin subsequently, since it becomes completely inelastic. Focused ultrasound became the first major claim to victory when Ulthera was able to prove lifting of sagging eyebrows after the procedure. The method is that ultrasound is focused at the SMAS level, heating it up to the point of coagulation. Yes, yes, we are talking about again thermal burn. But the difference with fractional lasers is that the surface layers of the skin do not overheat. The method can be classified as fractional, since not the entire SMAS overheats, but hundreds of “hot spots” are created. Within these points, overheating causes scarring, which reduces tissue volume. Yes, the procedure is very painful. And scars are not very good, because fibrous tissue is deprived of normal nutrition and blood supply, which worsens the quality of the skin over time. A number of patients, as a side effect, note a reduction in the subcutaneous fat layer, which makes the facial features look sharp like an old man... And finally, the latest development of scientists is the RecoSMA technology. It belongs to laser, but is non-thermal (the skin remains at 36.6 C during the procedure). In this case, the impact goes to a depth of up to 6 mm, which is beyond the power of any other laser. The skin is not damaged, maintaining its protective properties. Just a few days after the procedure, you can sunbathe without fear of pigmentation. And most importantly, here skin tightening is achieved not through scarring, as in other cases. The skin is actually renewed, becoming younger in all respects. A study recently conducted at the French public hospital Henri Mondor convincingly proved the capabilities of the new technology (read about it here) So, today you have a choice - “tighten and cut off the excess” or “really rejuvenate”. RecoSMA or plastic surgery? Compare and make your choice! RecoSMA does not provide as fast and as radical a result as plastic surgery. Laser rejuvenation gives a “impetus” to the body, and it begins to produce collagen and change the structure of the skin. The effect appears after about a month and then increases over six months. But this procedure has much more advantages. 1. RecoSMA is a natural tightening. Not required surgical intervention. The body does everything itself. 2. RecoSMA is a risk-free lift. You do not risk changing your appearance beyond recognition or getting the wrong result that you wanted. 3. RecoSMA is a safe lift. There are no scars or other marks left on the skin that a surgeon’s scalpel can leave. 4. RecoSMA is tolerated comfortably. Even local anesthesia is not required. During the procedure, you only feel a warm tingling sensation. 5. RecoSMA does not require rehabilitation. Light redness goes away the next day, then the skin begins to actively peel off. No special care is required, and after 4-5 days you can return to your normal lifestyle. 6. In addition to the tightening effect, RekoSMA really rejuvenates the skin. It removes skin defects such as scars, post-acne, etc. Enlarged pores narrow, which prevents them from clogging and the formation of blackheads in the future. One RecoSMA treatment per year and you may never need to go under the knife. Many of our clients note that with RekoSMA they seem to have stopped time. Choose the best for beauty and health! Photos before and after the procedure:
To
After
David Kochiev, Ivan Shcherbakov
"Nature" No. 3, 2014
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David Georgievich Kochiev— Candidate of Physical and Mathematical Sciences, Deputy Director of the Institute general physics them. A. M. Prokhorov RAS for scientific work. Area of scientific interests: laser physics, lasers for surgery. |
Ivan Aleksandrovich Shcherbakov— Academician, Academician-Secretary of the Department of Physical Sciences of the Russian Academy of Sciences, Professor, Doctor of Physical and Mathematical Sciences, Director of the Institute of General Physics of the Russian Academy of Sciences, Head of the Department of Laser Physics of Moscow Institute of Physics and Technology. Awarded a gold medal named after. A. M. Prokhorov RAS (2013). He works in laser physics, spectroscopy, nonlinear and quantum optics, and medical lasers. |
The unique ability of a laser to concentrate energy as much as possible in space, time and in the spectral range makes this device an indispensable tool in many areas of human activity, and in particular in medicine [,]. When treating diseases, there is intervention in the pathological process or painful condition, which is the most radical practice of surgery. Thanks to progress in science and technology, mechanical surgical instruments are being replaced by fundamentally different ones, including laser ones.
If laser radiation is used as a tool, then its task is to cause changes in biological tissue (for example, to perform resection during surgery, to trigger chemical reactions during photodynamic therapy). The parameters of laser radiation (wavelength, intensity, duration of exposure) can vary over a wide range, which, when interacting with biological tissues, makes it possible to initiate the development of various processes: photochemical changes, thermal and photodestruction, laser ablation, optical breakdown, generation of shock waves, etc.
In Fig. 1 shows the wavelengths of lasers that have found application in varying degrees medical practice. Their spectral range extends from the ultraviolet (UV) to the mid-infrared (IR) region, and the energy density range covers 3 orders of magnitude (1 J/cm 2 - 10 3 J/cm 2), the power density range covers 18 orders of magnitude (10 −3 W /cm 2 - 10 15 W/cm 2), time range - 16 orders, from continuous radiation (~ 10 s) to femtosecond pulses (10 −15 s). The processes of interaction of laser radiation with tissue are determined by the spatial distribution of the volumetric energy density and depend on the intensity and wavelength of the incident radiation, as well as on the optical properties of the tissue.
At the first stages of the development of laser medicine, biological tissue was represented as water with “impurities,” since a person consists of 70–80% water and it was believed that the mechanism of action of laser radiation on biological tissue was determined by its absorption. When using continuous wave lasers, this concept was more or less workable. If it is necessary to organize exposure to the surface of biological tissue, one should choose a wavelength of radiation that is strongly absorbed by water. If a volumetric effect is required, on the contrary, the radiation should be weakly absorbed by it. However, as it turned out later, other components of biological tissue are also capable of absorbing (in particular, in the visible region of the spectrum - blood components, Fig. 2). The understanding has come that biological tissue is not water with impurities, but a much more complex object.
At the same time, pulsed lasers began to be used. The effect on biological tissues is determined by a combination of wavelength, energy density and radiation pulse duration. The latter factor, for example, helps to separate thermal and non-thermal effects.
Pulsed lasers with a wide range of pulse duration variations - from milli- to femtoseconds - have come into practice. Here various nonlinear processes come into play: optical breakdown on the target surface, multiphoton absorption, formation and development of plasma, generation and propagation of shock waves. It became obvious that it is impossible to create a single algorithm for searching for the desired laser and each specific case requires a different approach. On the one hand, this made the task extremely difficult, on the other hand, it opened up absolutely fantastic opportunities to vary the methods of influencing biological tissue.
When radiation interacts with biological tissues great value has scattering. In Fig. Figure 3 shows two specific examples of the distribution of radiation intensity in the tissues of the dog’s prostate gland when laser radiation with different wavelengths is incident on its surface: 2.09 and 1.064 microns. In the first case, absorption prevails over scattering, in the second the situation is the opposite (Table 1).
In the case of strong absorption, the penetration of radiation obeys the Bouguer-Lambert-Beer law, i.e., exponential decay occurs. In the visible and near-IR wavelength ranges, typical values of the scattering coefficients of most biological tissues lie in the range of 100–500 cm −1 and monotonically decrease with increasing radiation wavelength. With the exception of the UV and far-IR regions, the scattering coefficients of biological tissue are one to two orders of magnitude greater than the absorption coefficient. Under conditions of dominance of scattering over absorption, a reliable picture of the propagation of radiation can be obtained using the diffuse approximation model, which, however, has quite clear limits of applicability that are not always taken into account.
Table 1. Parameters of laser radiation and optical characteristics of dog prostate tissue
So, when using a particular laser for specific operations, a number of nonlinear processes and the ratio of scattering and absorption should be taken into account. Knowledge of the absorbing and scattering properties of the selected tissue is necessary for calculating the distribution of radiation within the biological environment, determining the optimal dosage, and planning the results of exposure.
Let us consider the main types of interaction of laser radiation with biological tissues, realized when using lasers in clinical practice.
The photochemical mechanism of interaction plays a major role in photodynamic therapy, when selected chromophores (photosensitizers) are introduced into the body. Monochromatic radiation initiates selective photochemical reactions with their participation, triggering biological transformations in tissues. After resonant excitation by laser radiation, the photosensitizer molecule experiences several synchronous or sequential decays, which cause intramolecular transfer reactions. As a result of a chain of reactions, a cytotoxic reagent is released, irreversibly oxidizing the main cellular structures. The impact occurs at low radiation power densities (~1 W/cm 2) and for long periods of time (from seconds to continuous irradiation). In most cases, laser radiation of the visible wavelength range is used, which has a large penetration depth, which is important when it is necessary to influence deep-lying tissue structures.
If photochemical processes occur due to the flow of a chain of specific chemical reactions, then thermal effects when exposed to laser radiation on tissue are, as a rule, not specific. At the microscopic level, volumetric absorption of radiation occurs due to transitions in molecular vibrational-rotational zones and subsequent non-radiative attenuation. The tissue temperature is raised very efficiently because photon absorption is facilitated by the huge number of available vibrational levels of most biomolecules and the many possible collision relaxation channels. Typical photon energy values are: 0.35 eV - for Er:YAG lasers; 1.2 eV - for Nd:YAG lasers; 6.4 eV for ArF lasers and significantly exceeds the kinetic energy of the molecule, which at room temperature is only 0.025 eV.
Thermal effects in tissue play a dominant role when using lasers with continuous mode generation and pulsed lasers, with pulse durations of several hundred microseconds or more (lasers in the free generation mode). Removal of tissue begins after heating its surface layer to a temperature above 100°C and is accompanied by an increase in pressure in the target. Histology at this stage shows the presence of breaks and the formation of vacuoles (cavities) within the volume. Continued irradiation leads to an increase in temperature to 350–450°C, and burnout and carbonization of the biomaterial occurs. Thin layer carbonized tissue (≈20 µm) and a layer of vacuoles (≈30 µm) maintain a high pressure gradient along the tissue removal front, the speed of which is constant over time and depends on the type of tissue.
During pulsed laser exposure, the development of phase processes is influenced by the presence of the extracellular matrix (ECM). Boiling of water inside the tissue volume occurs when the difference in the chemical potentials of the vapor and liquid phase, necessary for the growth of bubbles, exceeds not only the surface tension at the interface, but also the elastic stretching energy of the ECM necessary to deform the matrix of the surrounding tissue. Bubble growth in tissue requires greater internal pressure than in pure liquid; An increase in pressure leads to an increase in boiling point. The pressure increases until it exceeds the tensile strength of the ECM tissue and causes tissue to be removed and ejected. Thermal damage to tissue can range from carbonization and melting at the surface to hyperthermia several millimeters deep, depending on the power density and exposure time of the incident radiation.
A spatially limited surgical effect (selective photothermolysis) is carried out with a pulse duration shorter than the characteristic time of thermal diffusion of the heated volume - then the heat is retained in the area of influence (does not move even to a distance equal to the optical depth of penetration), and thermal damage to surrounding tissues is small. Exposure to radiation from continuous lasers and lasers with long pulses (duration ≥100 μs) is accompanied by a larger area of thermal damage to tissues adjacent to the area of exposure.
Reducing the pulse duration changes the picture and dynamics of thermal processes during the interaction of laser radiation with biological tissues. When accelerating the supply of energy to a biomaterial, its spatial distribution is accompanied by significant thermal and mechanical transient processes. By absorbing the energy of photons and heating up, the material expands, tending to enter a state of equilibrium in accordance with its thermodynamic properties and with external conditions environment. The resulting inhomogeneity of the temperature distribution gives rise to thermoelastic deformations and a compression wave propagating through the material.
However, expansion or establishment of mechanical equilibrium in response to tissue heating takes a characteristic time equal in order of magnitude to the time required for a longitudinal acoustic wave to travel through the system. When the laser pulse duration exceeds this, the material expands during the pulse and the induced pressure value changes with the intensity of the laser radiation. In the opposite case, energy input into the system occurs faster than it can mechanically respond to it, and the expansion rate is determined by the inertia of the heated tissue layer, regardless of the radiation intensity, and the pressure changes along with the value of the volumetric energy absorbed in the tissue. If we take a very short pulse (with a duration much shorter than the travel time of the acoustic wave across the heat generation region), the tissue will be “inertially held,” i.e., it will not receive time to expand, and heating will occur at a constant volume.
When the rate of energy release in the tissue volume upon absorption of laser radiation is much higher than the rate of energy loss due to evaporation and normal boiling, the water in the tissue passes into a superheated metastable state. When approaching the spinodal, the fluctuation mechanism of nucleation (homogeneous nucleation) comes into play, which ensures the rapid decomposition of the metastable phase. The process of homogeneous nucleation manifests itself most clearly during pulsed heating of the liquid phase, which is expressed in the explosive boiling of the superheated liquid (phase explosion).
Laser radiation can also directly destroy biomaterials. The dissociation energy of chemical bonds of organic molecules is less than or comparable to the energy of photons of laser radiation in the UV range (4.0–6.4 eV). When tissue is irradiated, such photons, absorbed by complex organic molecules, can cause direct rupture of chemical bonds, causing “photochemical decomposition” of the material. The interaction mechanism in the laser pulse duration range of 10 ps - 10 ns can be classified as electromechanical, which implies the generation of plasma in an intense electric field (optical breakdown) and tissue removal due to the propagation of shock waves, cavitation and the formation of jets.
The formation of plasma on the surface of the tissue is characteristic of short durations pulse at radiation intensities of the order of 10 10 –10 12 W/cm 2, corresponding to a local electric field strength of ~10 6 –10 7 V/cm. In materials that experience an increase in temperature due to a high absorption coefficient, plasma can arise and be maintained due to the thermal emission of free electrons. In environments with low absorption, it is formed at high radiation intensities due to the release of electrons during multiphoton absorption of radiation and avalanche-like ionization of tissue molecules (optical breakdown). Optical breakdown allows you to “pump” energy not only into well-absorbing pigmented tissues, but also into transparent, weakly absorbing tissues.
Removal of tissue when exposed to pulsed laser radiation requires destruction of the ECM and cannot be considered simply as a process of dehydration during heating. Pressures generated during phase explosion and limited boiling lead to destruction of ECM tissue. The result is an explosive release of material without complete evaporation. The energy threshold of such a process turns out to be lower than the specific enthalpy of water vaporization. Fabrics with high tensile strength require higher temperatures to destroy the ECM (threshold volumetric energy density must be comparable to the enthalpy of vaporization).
One of the most common surgical lasers is the Nd:YAG laser, used for interventions with endoscopic access in pulmonology, gastroenterology, urology, in aesthetic cosmetology for hair removal, and for interstitial laser coagulation of tumors in oncology. In Q-switched mode, with pulse durations from 10 ns, it is used in ophthalmology, for example in the treatment of glaucoma.
Most tissues at its wavelength (1064 nm) have a low absorption coefficient. The effective depth of penetration of such radiation into tissue can be several millimeters and ensures good hemostasis and coagulation. However, the volume of removed material is relatively small, and tissue dissection and ablation may be accompanied by thermal damage to nearby areas, swelling and inflammatory processes.
An important advantage of the Nd:YAG laser is the ability to deliver radiation to the affected area using fiber-optic light guides. The use of endoscopic and fiber instruments makes it possible to conduct laser radiation into the lower and upper sections gastrointestinal tract in a virtually non-invasive way. Increasing the pulse duration of this laser in Q-switched mode to 200–800 ns made it possible to use thin optical fibers with a core diameter of 200–400 μm for stone fragmentation. Unfortunately, absorption in the optical fiber prevents the delivery of laser radiation at wavelengths more effective for tissue ablation, such as 2.79 μm (Er:YSGG) and 2.94 μm (Er:YAG). To transport radiation with a wavelength of 2.94 microns at the Institute of General Physics (IOF) named after. A. M. Prokhorov RAS developed an original technology for the growth of crystalline fibers, with the help of which a unique crystalline fiber from leucosapphire was produced, which passed successful tests. Transport of radiation through commercially available light guides is possible for radiation with shorter wavelengths: 2.01 μm (Cr:Tm:YAG) and 2.12 μm (Cr:Tm:Ho:YAG). The penetration depth of radiation of these wavelengths is small enough for effective ablation and minimization of associated thermal effects (it is ~170 μm for a thulium laser and ~350 μm for a holmium laser).
Dermatology has adopted lasers in both the visible (ruby, alexandrite, lasers with second harmonic generation by nonlinear crystals of potassium titanyl phosphate, KTP) and infrared wavelengths (Nd:YAG). Selective photothermolysis is the main effect used in laser treatment of skin tissue; indications for treatment - various vascular skin lesions, benign and malignant tumors, pigmentation, tattoo removal and cosmetic interventions.
ErCr:YSGG (2780 nm) and Er:YAG (2940 nm) lasers are used in dentistry to influence hard dental tissues in the treatment of caries and preparation of the dental cavity; During manipulation there are no thermal effects, damage to the tooth structure and discomfort for the patient. KTP, Nd:YAG, ErCr:YSGG and Er:YAG lasers are used in surgery on soft tissues of the oral cavity.
Historically, the first area of medicine to master the new tool was ophthalmology. Work related to laser welding of the retina began in the late 1960s. The concept of “laser ophthalmology” has become commonly used; it is impossible to imagine a modern clinic of this profile without the use of lasers. Light welding of the retina has been discussed for many years, but it was only with the advent of laser sources that retinal photocoagulation entered into widespread routine clinical practice.
In the late 70s - early 80s of the last century, work began with lasers based on a pulsed Nd:YAG laser to destroy the lens capsule in the case of secondary cataract. Today, capsulotomy, performed using a Q-switched neodymium laser, is the standard surgical procedure for the treatment of this disease. A revolution in ophthalmology was made by the discovery of the ability to change the curvature of the cornea using short-wave UV radiation and thus correct visual acuity. Laser operations for vision correction are now widespread and performed in many clinics. Significant progress in refractive surgery and in a number of other minimally invasive microsurgical interventions (corneal transplantation, creation of intrastromal canals, treatment of keratoconus, etc.) was achieved with the introduction of lasers with short and ultra-short pulse durations.
Currently, in ophthalmic practice, the most popular are solid-state Nd:YAG and Nd:YLF lasers (continuous, pulsed, Q-switched with pulse durations of the order of several nanoseconds, and femtosecond), and to a lesser extent, Nd:YAG lasers with a wavelength of 1440 nm. in free-running mode, Ho- and Er-lasers.
Since different parts of the eye have different compositions and different absorption coefficients for the same wavelength, the choice of the latter determines both the segment of the eye where the interaction will occur and the local effect in the focusing area. Based on the spectral transmission characteristics of the eye, it is advisable to use lasers with a wavelength in the range of 180–315 nm for surgical treatment of the outer layers of the cornea and anterior segment. Deeper penetration, right up to the lens, can be achieved in the spectral range of 315–400 nm, and for all distant regions, radiation with a wavelength of more than 400 nm and up to 1400 nm is suitable, when significant absorption of water begins.
Based on taking into account the properties of biological tissues and the type of interaction realized during incident radiation, the Institute of General Physics develops laser systems for use in various fields of surgery, collaborating with many organizations. The latter include academic institutes (Institute for Laser and information technology- IPLIT, Institute of Spectroscopy, Institute of Analytical Instrumentation), Moscow State University. M.V. Lomonosov, leading medical centers of the country (MNTK "Eye Microsurgery" named after S.N. Fedorov, Moscow Scientific Research Oncology Institute named after P.A. Herzen of the Russian Health Service, Russian Medical Academy of Postgraduate Education, Science Center Cardiovascular Surgery named after. A. N. Bakuleva RAMS, Central Clinical Hospital No. 1 of JSC Russian Railways), as well as a number of commercial companies (“Optosystems”, “Visionics”, “New Energy Technologies”, “Laser Technologies in Medicine”, “Cluster”, STC “Fiber Optical Systems” ").
Thus, our institute has created a laser surgical complex “Lazurit”, which can act as both a scalpel-coagulator and a lithotripter, i.e. a device for destroying stones in human organs. Moreover, the lithotripter operates on a new original principle - radiation with two wavelengths is used. This is a laser based on an Nd:YAlO 3 crystal (with a main radiation wavelength of 1079.6 nm and its second harmonic in the green region of the spectrum). The installation is equipped with a video processing unit and allows you to monitor the operation in real time.
Two-wave laser exposure of microsecond duration provides a photoacoustic mechanism of stone fragmentation, which is based on the optical-acoustic effect discovered by A. M. Prokhorov and his colleagues - the generation of shock waves during the interaction of laser radiation with a liquid. The impact turns out to be nonlinear [, ] (Fig. 4) and includes several stages: optical breakdown on the surface of the stone, formation of a plasma spark, development of a cavitation bubble and propagation of a shock wave during its collapse.
As a result, after ~700 μs from the moment the laser radiation falls on the surface of the stone, the latter is destroyed due to the impact of the shock wave generated during the collapse of the cavitation bubble. The advantages of this method of lithotripsy are obvious: firstly, it ensures the safety of the impact on the soft tissue surrounding the stone, since the shock wave is not absorbed in them and, therefore, does not cause them the harm inherent in other laser lithotripsy methods; secondly, high efficiency is achieved in fragmenting stones of any location and chemical composition (Table 2); thirdly, a high rate of fragmentation is guaranteed (see Table 2: the duration of destruction of stones varies in the range of 10–70 s depending on their chemical composition); fourthly, the fiber instrument is not damaged during radiation delivery (due to the optimally selected pulse duration); finally, the number of complications is radically reduced and the postoperative treatment period is shortened.
Table 2. Chemical composition of stones and parameters of laser radiation during fragmentation in experiments in vitro
The Lazurit complex (Fig. 5) also includes a scalpel-coagulator, which allows, in particular, to successfully perform unique operations on blood-filled organs, such as the kidney, to remove tumors with minimal blood loss, without compressing the renal vessels and without creating artificial ischemia organ accompanying currently accepted methods of surgical intervention. Resection is performed using a laparoscopic approach. With an effective penetration depth of pulsed one-micron radiation of ~1 mm, tumor resection, coagulation and hemostasis are simultaneously carried out, and ablasticity of the wound is achieved. A new medical technology for laparoscopic kidney resection for T 1 N 0 M 0 cancer has been developed.
The results of research work in the field of ophthalmology were the development of ophthalmic laser systems “Microscan” and its modification “Microscan Visum” for refractive surgery based on an ArF excimer laser (193 nm). Using these settings, myopia, farsightedness and astigmatism are corrected. The so-called “flying spot” method is implemented: the cornea of the eye is illuminated by a spot of radiation with a diameter of about 0.7 mm, which scans its surface according to an algorithm specified by a computer and changes its shape. Vision correction by one diopter at a pulse repetition rate of 300 Hz is provided in 5 s. The effect remains superficial, since radiation with this wavelength is strongly absorbed by the cornea of the eye. The eye tracking system allows you to provide high quality operations regardless of the patient's eye mobility. The Microscan installation is certified in Russia, the CIS countries, Europe and China; 45 Russian clinics are equipped with it. Ophthalmic excimer systems for refractive surgery, developed at our institute, currently occupy 55% of the domestic market.
Supported by Federal agency For science and innovation, with the participation of the Institute of General Physics of the Russian Academy of Sciences, IPLIT RAS and Moscow State University, an ophthalmological complex was created, which includes the Microscan Visum, diagnostic equipment consisting of an aberrometer and a scanning ophthalmoscope, as well as a unique femtosecond laser ophthalmological system Femto Visum. The birth of this complex became an example of fruitful cooperation between academic organizations and the Moscow state university within the framework of a single program: a surgical instrument was developed at the IOF, and diagnostic equipment was developed at Moscow State University and IPLIT, which allows for a number of unique ophthalmological operations. The principle of operation of the femtosecond ophthalmological unit should be discussed in more detail. A neodymium laser with a radiation wavelength of 1064 nm was chosen as its basis. If, when using an excimer laser, the cornea absorbs strongly, then at a wavelength of ~1 μm the linear absorption is weak. However, due to the short pulse duration (400 fs) when focusing the radiation, it is possible to achieve a high power density, and, consequently, multiphoton processes become effective. By organizing appropriate focusing, it becomes possible to influence the cornea in such a way that its surface is not affected in any way, and multiphoton absorption occurs in the volume. The mechanism of action is photodestruction of corneal tissue during multiphoton absorption (Fig. 6), when there is no thermal damage to nearby layers of tissue and intervention can be carried out with precision accuracy. If for excimer laser radiation the photon energy (6.4 eV) is comparable to the dissociation energy, then in the case of one-micron radiation (1.2 eV) it is at least half, or even seven times less, which ensures the described effect and opens new opportunities in laser ophthalmology.
Today, photodynamic diagnostics and cancer therapy are intensively developing based on the use of a laser, the monochromatic radiation of which excites the fluorescence of a photosensitizer dye and initiates selective photochemical reactions that cause biological transformations in tissues. Doses of dye administration are 0.2–2 mg/kg. In this case, the photosensitizer predominantly accumulates in the tumor, and its fluorescence makes it possible to determine the localization of the tumor. Due to the effect of energy transfer and an increase in laser power, singlet oxygen is formed, which is a strong oxidizing agent, which leads to the destruction of the tumor. Thus, according to the described method, not only diagnosis is carried out, but also treatment oncological diseases. It should be noted that the introduction of a photosensitizer into the human body is not a completely harmless procedure and therefore in some cases it is better to use the so-called laser-induced autofluorescence. It turned out that in some cases, especially with the use of short-wave laser radiation, healthy cells do not fluoresce, while cancer cells exhibit a fluorescent effect. This technique is preferable, but for now it serves mainly diagnostic purposes(although recently steps have been taken to implement therapeutic effect). Our institute has developed a series of devices for both fluorescence diagnostics and photodynamic therapy. This equipment is certified and mass-produced; 15 Moscow clinics are equipped with it.
For endoscopic and laparoscopic operations, a necessary component of a laser installation is the means of delivering radiation and forming its field in the area of interaction. We have designed such devices based on multimode optical fibers, allowing operation in the spectral region from 0.2 to 16 microns.
With the support of the Federal Agency for Science and Innovation, the IOF is developing a technique for searching for the size distribution of nanoparticles in liquids (and in particular in human blood) using quasi-elastic light scattering spectroscopy. It was found that the presence of nanoparticles in a liquid leads to broadening of the central peak of Rayleigh scattering, and measuring the magnitude of this broadening makes it possible to determine the size of the nanoparticles. A study of the size spectra of nanoparticles in the blood serum of patients with cardiovascular disorders showed the presence of protein-lipid clusters large sizes(Fig. 7). It was also found that large particles are also characteristic of the blood of cancer patients. Moreover, when positive result treatment, the peak responsible for large particles disappeared, but in case of relapse it reappeared. Thus, the proposed technique is very useful for diagnosing both oncological and cardiovascular diseases.
Previously, the institute developed new method detection of extremely low concentrations of organic compounds. The main components of the device were a laser, a time-of-flight mass spectrometer, and a nanostructured plate on which the gas under study was adsorbed. Today, this installation is being modified for blood analysis, which will also open up new opportunities for the early diagnosis of many diseases.
A range of solutions medical problems is possible only by combining efforts in several areas: this and basic research in laser physics, and a detailed study of the interaction of radiation with matter, and analysis of energy transfer processes, and medical and biological research, and development medical technologies treatment.
4 YSGG - Yttrium Scandium Gallium Garnet(yttrium scandium gallium garnet).
YLF- Yttrium Lithium Fluoride(yttrium lithium fluoride).
Lasers have long been used in surgical practice, and many clinics are actively using this technology. But patients still wonder how painless and effective it is? Deputy Chief Physician for Surgery of the MEGI network of clinics for adults and children, Doctor of Sciences Aidar Gallyamov gave an interview to the ProUfu.ru newspaper and answered this question.
– How does a medical laser work?
– A laser device is a unique device that emits thin bunch Sveta. It contains a huge amount of energy that can cut and weld tissue and stop bleeding. The so-called laser scalpel is based on this operating principle.
Using a laser is actually painless and effective, because it provides:
1. The operation is bloodless, since when making an incision, the edges of the dissected tissues are coagulated and the dissected blood vessels are sealed. Blood loss is practically zero.
2. The accuracy of the surgeon's work. The cut line turns out to be absolutely even, regardless of the density of the tissue (for example, when it hits dense tissue or a bone area, the beam, unlike a conventional scalpel, does not deviate to the side).
3. Complete sterility, it is achieved due to the fact that when manipulating the laser there is no contact with tissues, in addition, the radiation has an antibacterial and antiseptic effect.
4. Painless. Laser treatment is virtually painless and does not require long postoperative rehabilitation.
– There is an opinion that with the help of a laser you can only remove moles, papillomas and treat varicose veins, is this true?
- Only partly. It all depends on the clinic. Some specialize only in data laser procedures, others use laser for more wide range operations. In any case, it is very important which medical laser center you choose. The main thing is that the clinic has the most modern equipment. In Ufa, the MEGI network of clinics for adults and children recently opened a Center laser surgery. This center presents the latest devices: seven semiconductor laser systems, four of them from IPG (“IPG”) - the best in the world in terms of quality and equipment capabilities.
- What is it like? medical use laser radiation in your center?
– Using laser machines at MEGI, you can be provided with medical care in the following areas: proctology, urology, gynecology, mammology, surgery, phlebology.
In proctology, hemorrhoids are removed with a laser, fissures in the anal canal are excised, neoplasms of the rectum (polyps and condylomas) are removed; it is with the help of a laser that minimally invasive operations are performed, vaporization of hemorrhoids without a single incision.
In urology, endourological laser removal of polyps and tumors is performed bladder, neoplasms of the urogenital area (polyps and condylomas), used when performing circumcision. Using a laser to destroy stones in urinary tract, this is called contact laser lithotripsy.
In gynecology, lasers are used to remove uterine fibroids and perform ovarian surgeries. It is also used in the treatment of cervical erosion and removal of tumors.
In mammology, almost all operations are performed using laser systems. At cystic mastopathy The puncture method of treatment is widely used - laser ablation of cysts and other neoplasms of the mammary glands.
In surgery, neoplasms of the skin and soft tissues (papillomas, various moles, atheromas, lipomas, fibromas) are removed; used in operations in abdominal cavity(at endoscopic operations, the laser is indispensable for operations on the liver, spleen, pancreas), removing age spots and tattoos.
In phlebology, lasers are used to treat varicose veins, phlebectomy, laser radiofrequency obliteration of veins and “ spider veins", as well as sclerotherapy.
– How to decide to undergo medical laser surgery?
– As a surgeon, I affirm that there is no need to be afraid of the laser. If you have chosen good clinic With modern operating rooms, where surgical treatments are carried out quickly and painlessly for the patient, you can be sure of an excellent result. Our MEGI center has created all the conditions for this. If necessary and desired, early postoperative period the patient can spend a certain time in the ward under the supervision of experienced medical staff.
